This research aims at developing bioresorbable polylactide/calcium phosphate composites with significantly improved mechanical properties by using surface initiated polymerization combined with phosphonic based coupling agents. Bioresorbable composite made from degradable polymer and bioactive calcium phosphates are clinically desirable for bone fixation, repair and tissue engineering, because they do not need to be removed by surgery after the bone heals. However, due to the hydrophobicity of the polymer matrix and hydophilicity of the calcium phosphates, the interfacial adhesion between the two phases within the current available composites is relatively weak, leading to weak mechanical properties of these composites. In order to improve the interfacial interaction, a surface initiated polymerization will be developed to establish direct chemical bond between the polymer and the calcium phosphate filler. A special chelating coupling molecule based on phosphonic acid instead of the conventional silanes or carboxylic acids will be employed to improve the binding. By combining the special chelating coupling agent and surface initiated polymerization, we expect that bioresorbable composites with significantly improved interfacial adhesion and improved mechanical properties can be developed. Scientifically, success of the proposed research will provide a widely useful route to improve the performance of composite materials, specifically based on osteoconductive calcium phosphates. Clinically, such bioresorbable materials with improved mechanical properties should have wide applications to bone fixation and repair.